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体验新版 GitCode,发现更多精彩内容 >>
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93bb57e7
编写于
8月 11, 2015
作者:
A
Alex Crichton
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rollup merge of #27605: AlisdairO/diagnostics387
As title :-) Part of #24407. r? @Manishearth
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58b0aa5e
f0419661
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+54
-1
src/librustc_borrowck/diagnostics.rs
src/librustc_borrowck/diagnostics.rs
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未找到文件。
src/librustc_borrowck/diagnostics.rs
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93bb57e7
...
...
@@ -158,6 +158,60 @@ fn main(){
x = 5;
}
```
"##
,
E0387
:
r##"
This error occurs when an attempt is made to mutate or mutably reference data
that a closure has captured immutably. Examples of this error are shown below:
```
// Accepts a function or a closure that captures its environment immutably.
// Closures passed to foo will not be able to mutate their closed-over state.
fn foo<F: Fn()>(f: F) { }
// Attempts to mutate closed-over data. Error message reads:
// `cannot assign to data in a captured outer variable...`
fn mutable() {
let mut x = 0u32;
foo(|| x = 2);
}
// Attempts to take a mutable reference to closed-over data. Error message
// reads: `cannot borrow data mutably in a captured outer variable...`
fn mut_addr() {
let mut x = 0u32;
foo(|| { let y = &mut x; });
}
```
The problem here is that foo is defined as accepting a parameter of type `Fn`.
Closures passed into foo will thus be inferred to be of type `Fn`, meaning that
they capture their context immutably.
If the definition of `foo` is under your control, the simplest solution is to
capture the data mutably. This can be done by defining `foo` to take FnMut
rather than Fn:
```
fn foo<F: FnMut()>(f: F) { }
```
Alternatively, we can consider using the `Cell` and `RefCell` types to achieve
interior mutability through a shared reference. Our example's `mutable` function
could be redefined as below:
```
use std::cell::Cell;
fn mutable() {
let x = Cell::new(0u32);
foo(|| x.set(2));
}
```
You can read more about cell types in the API documentation:
https://doc.rust-lang.org/std/cell/
"##
}
...
...
@@ -166,7 +220,6 @@ fn main(){
E0383
,
// partial reinitialization of uninitialized structure
E0385
,
// {} in an aliasable location
E0386
,
// {} in an immutable container
E0387
,
// {} in a captured outer variable in an `Fn` closure
E0388
,
// {} in a static location
E0389
// {} in a `&` reference
}
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